When did the Gregorian calendar start?
Quick Answer: The Gregorian calendar officially started on October 15, 1582, when Pope Gregory XIII introduced it to replace the Julian calendar and correct calendar drift.
The Julian calendar, used before the Gregorian, had a small error in calculating leap years. Over centuries, this caused the calendar dates to drift away from the seasons. To fix this, Pope Gregory XIII introduced the Gregorian calendar with a new system for leap years and skipped 10 days to realign the calendar.
The change was first adopted by Catholic countries in 1582, but other countries switched gradually over the following centuries. Today, the Gregorian calendar is the most widely used civil calendar worldwide.